Certain welding methods needed to take place in a neutral atmosphere which can be effected by containing the welding machine and the elements to be welded in a chamber or by blowing the neutral gas in a sheath surrounding the energy beam and the molten zone. The consumption of gas is significant in both cases, as the volume of the chamber or the blowing flowrate needs to be considerable. This is why in the present invention another solution has been put forward and in this case containment is obtained by a box partially integral with the welding head and traversed by the welding head. This box can be placed solely on a portion of the elements to be welded so as to cover the welding joint, although it can also fully surround these elements. The gas is therefore confined in a closed volume but with a much smaller volume than a chamber which would contain the entire machine; and although the box needs to be open so as to give passage to the welding head and possibly to cover only one portion of the elements to be welded, there is no need to blow an extremely small amount of protection gas as leaks are negligible.